Endovascular stent and delivery system

ABSTRACT

A wire stent for insertion and expansion into a passageway comprises a plurality of curved sections that are formed into a generally circular configuration. Adjacent curved sections are joined by a bend or cusp, so that a series of alternating opposing loops are formed. The wire stent as formed has a cylindrical shape with a longitudinal opening through which a folded balloon catheter is inserted. The opposing loops are tightly contracted about the catheter so that the cylindrical shape has an overlapping region in which portions of adjacent loops longitudinally overlap. The loops are arranged so that when the balloon catheter is inflated, adjacent loops diverge circumferentially relative to each other, thereby decreasing the overlapping region while increasing the diameter of the cylindrical shape. As the diameter of the cylindrical shape increases, the wire stent contacts the surface of a passageway in which the stent is inserted. 
     In a method of the present invention, the wire stent is fabricated from a wire formed into a planar serpentine configuration. The wire is centered over a semi-cylindrical trough in a flat plate and then pressed into the trough by a forming bar so that a portion of the wire assumes the semi-cylindrical shape. A pulling tool, having a hook at one end, is engaged at the hook with the exposed loops of the serpentine configuration for pulling the exposed loops over the exposed portion of the forming bar to form a generally cylindrical shape from the wire. Once the wire is extracted from the trough and the forming bar is removed, a folded balloon catheter is inserted through the cylindrical shape and the wire is tightly pressed about the catheter.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 666,211 filed Mar. 7,1991, now abandoned, which is a continuation of Ser. No. 244,669 filedSep. 14, 1988, now U.S. Pat. No. 5,041,126 which is a continuation ofSer. No. 25,736 filed Mar. 13, 1987, now U.S. Pat. No. 4,800,882.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to stents and a method for inserting a stent.

2. Description of the Prior Art

It is desirable in various situations to provide means for expanding aconstricted vessel or for maintaining an open passageway through avessel. Such situations arise, for instance, after an angioplasty of acoronary artery. In these situations, wire stents are useful to preventrestenosis of the dilated vessel, or to eliminate the danger ofocclusion caused by "flaps" resulting from intimal tears associated withangioplasty. Wire stents can also be used to reinforce collapsingstructures in the respiratory and biliary tracts.

Typical of the wire stents of the prior art is the stent of Gianturco,U.S. Pat. No. 4,580,568, wherein the stent is compressed and encased ina sheath. The sheath is then positioned in the vascular system and thestent is held in position by a flat-ended pusher while the sheath iswithdrawn. The zig-zag configuration of this particular stent allows itto expand in the passageway to hold the passageway open and enlarged.

Stents comprised of variously shaped spiral springs are described byMaass et al. in U.S. Pat. No. 4,553,545, and in Radiology Follow-up ofTransluminally Inserted Vascular Endoprosthesis: An Experimental StudyUsing Expanding Spirals, Radiology, September 1984; 152: 659-663.Application of torque to the end of these spiral springs increases thenumber of coils while decreasing the stent diameter for insertion. Onceinserted, an opposite torque is applied to the spiral springs causingthe stent diameter to increase. Use of this type of stent requires asophisticated coaxial cable to apply torque to the stent once it hasbeen inserted into the vessel.

Dotter et al, reported the use of a prosthesis constructed of a thermalshape memory alloy which is passed into the passageway through acatheter. See, Dotter CT et al., Transluminal Expandable Nitinol CoilStent Grafting: Preliminary Report, Radiology, April, 1983; 147:259-260. This coil stent is compacted by cooling, inserted, and thenheated in situ until the stent expands in the passageway. This stent ispositioned within the vessel by a detachable positioning device capableof supplying electrical energy to heat the thermal coil.

Other references which may have relevance to the present invention arethe following U.S. patents: Abolins, U.S. Pat. No. 3,278,176; Alfidi etal., U.S. Pat. No. 3,868,956; Simon, U.S. Pat. No. 4,425,908; andSakura, Jr., U.S. Pat. No. 4,214,587.

Among the drawbacks of the prior art wire stents and expandable coilstents are that these stents are either difficult to produce orcomplicated to insert into a body passageway. Each of these stentsrequires the use of a complex device for insertion and expansion of thestent within the vessel. On the other hand, less complex wire stentslack the axial compliance to pass through a catheter that has anysignificant curves or bends. The present invention addresses each ofthese problems by providing a wire stent that is easy to produce, simpleto install and capable of delivery around curves and bends in a vesselor passageway.

SUMMARY OF THE INVENTION

A stent comprising a wire formed into a serpentine configurationincluding a series of straight sections and a plurality of bends. Thestraight sections are joined by the bends to form a series ofalternating loops. The serpentine configuration is formed into acylindrical shape having a longitudinal axis, wherein the straightsections are bent into generally circular configurations surrounding andgenerally perpendicular to the longitudinal axis. Means are provided forexpanding the circular configurations and, consequently, the cylindricalshape, comprising a balloon catheter. The balloon catheter is folded andreceived within the cylindrical shape and extends along the axis of thecylindrical shape. The straight sections are formed about the ballooncatheter such that adjacent loops diverge circumferentially relative toeach other as the balloon is inflated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a wire stent of the present invention.

FIG. 2 is an end view of the wire stent of FIG. 1.

FIG. 3 is a side view of the wire stent of FIG. 1 engaged around afolded balloon catheter and shown in the contracted condition.

FIG. 4 is a side view of the wire stent and balloon catheter of FIG. 3,shown in the expanded condition.

FIG. 5 is a fragmentary exploded view of a portion of a wire stent ofFIG. 1.

FIG. 6 is a cutaway view of a body cavity with the wire stent andballoon catheter situated in a curve in the cavity.

FIG. 7 is the cutaway view similar to FIG. 6 with the stent and ballooncatheter situated within the cavity adjacent an occlusion in the cavity.

FIG. 8 is the cutaway view of FIG. 7, shown with the balloon catheterinflated and with the stent in contact with the cavity wall to removethe occlusion.

FIG. 9 is a perspective view of a step of a method of the presentinvention showing a wire formed into a planar serpentine configurationand placed on a forming die.

FIG. 10 is a cross-sectional view of the forming die in FIG. 9 takenalong line 10--10 and viewed in the direction of the arrows.

FIG. 11 is a perspective view of the wire pressed into a trough in theforming die by a forming bar.

FIG. 12 is a cross-sectional view of the forming die and forming bar ofFIG. 11 taken along line 12--12 and viewed in the direction of thearrows.

FIG. 13 is a perspective view similar to FIG. 11 and showing the loopsof the serpentine configuration pulled over the exposed portion of theforming bar by pulling tools.

FIG. 14 is a cross-sectional view of the forming die and forming bar inFIG. 13 taken along line 14--14 and viewed in the direction of thearrows.

FIG. 15 is a perspective of a balloon catheter inserted through agenerally cylindrical opening formed by the wire in one step of thepresent method.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring to FIG. 1, a wire stent 10 is shown as having a longitudinalaxis 26. The stent comprises a plurality of curved sections 11 that aresituated generally perpendicular to the axis 26. Adjacent curvedsections 11 are joined by bends or cusps 13. A loop 18 is formed at eachfree end of the wire stent 10 in order to shield the wire end. Thecurved sections 11 are formed into a circular configuration, as shown inthe end view of FIG. 2, so that the stent 10 has a cylindrical opening12 formed therein.

The curved sections 11 and cusps 13 form a series of alternatingclockwise and counter-clockwise loops 15 and 16, respectively. Theclockwise direction relative to the axis 26 has been arbitrarilyselected and is noted by the heavy arrow 27 in FIG. 1. In the contractedcondition of the stent 10, these loops 15 and 16 overlap longitudinally,as demonstrated by the overlap region 20 shown in FIG. 3. Thus, theoverlap region 20 gives the appearance that the stent is a continuouscircular ring when viewed from an end, although when viewed as in FIGS.1 or 3 it is apparent that the cylindrical shape of the stent 10 isdiscontinuous. The importance of this feature is illustrated by acomparison of FIGS. 3 and 4.

In FIG. 3, the stent 10 is shown secured around a catheter 22, which hasan inflatable balloon 23 adhered thereon surrounding a feed orifice 22ain the catheter. The balloon used in this embodiment is a folded balloonin which flaps 23a of the balloon 23 are folded over the catheter 22, asshown in FIG. 3. The folded flaps 23a allow the balloon 23 to inflate toa specific diameter without excessively stretching the balloon materialand risking a rupture of the balloon:

The stent is compressed about the catheter 22 and balloon 23 so that itassumes a contracted outer diameter 24, which is calibrated to allowinsertion into a particular body passageway. The clockwise loops 15 andcounter-clockwise loops 16 overlap in the region 20, and the springstiffness of the wire keeps the stent in this position during insertion.The stent 10 remains in tight contact with the catheter 22 even as theassembly is delivered around curves and bends in a body passageway.

After the catheter and stent are fully inserted into the passageway, theballoon 23 is inflated to a diameter 25, which is calibrated to forcethe stent 10 into contact with the passageway inner surface and, atleast in some cases, to expand the passageway. As the balloon isinflated, the clockwise and counter-clockwise loops 15 and 16 divergecircumferentially until the longitudinal overlap between loops isreduced to the region 21, shown in FIG. 4. Thus, the effective diameterof the stent 10 relative to the longitudinal axis 26 is increasedwithout thermal expansion or application of torsional forces to thestent, as suggested in the prior art.

In the best mode of the invention, the wire comprising the stent 10 ismade of a malleable material, preferably from the group comprisingannealed stainless steel, tungsten and platinum. This malleable materialis sufficiently deformable to allow the loops 15 and 16 to diverge dueto radially outward pressure applied by inflation of the membrane thatcomprises the standard balloon catheter. Because the stent material isplastic, rather than elastic, the stent retains the enlarged diameterafter the balloon 23 is deflated and the catheter 22 removed. However,the material has sufficient strength and stiffness to avoid the stentbeing displaced on the balloon during insertion and to avoid the loops15 and 16 being forced into an overlying relation. Further, the stenthas sufficient strength and stiffness to allow it to maintain itsposition in the passageway and to resist being dislodged after thecatheter 22 has been removed and the balloon is no longer stabilizingthe stent. One example of a suitable wire has an outer diameter of0.0018 inches and is stainless steel AISI 316 alloy.

It is desirable that the overlap region 20 in the contracted conditionbe sufficiently large so that the stent has a high contact area with thecatheter, providing additional protection against the stent becomingdislodged while the assembly is inserted. In the expanded condition, theoverlap region 21 should be sufficiently large to provide continuouscircumferential support for the passageway in which the stent isinserted. In one example of the invention, the overlaying region 20extends almost 360° circumferentially. For clarity, the illustratedembodiment shows the overlap 20 to be substantially less.

It can be observed that applicant's preferred embodiment can bedissected into single coil helical sections. FIG. 5 is an exploded viewof a wire stent 49 having a longitudinal axis 50. The clockwisedirection, according to a right-hand rule, is denoted by the heavy arrow48 about the axis 50. The stent 49 comprises a series of alternatingsingle coil clockwise helical sections 51 and single coilcounter-clockwise helical sections 52. The helical sections 51 and 52have forward ends 51a and 52a, and aft ends 51b and 52b, respectively.The adjacent helical sections are joined by cusps 53, with the forwardend of one helical section being connected to the aft end of the nexthelical section. Thus, end 51a of the clockwise helical section 51 isjoined to end 52b of the counter-clockwise helical section 52, while end52a is connected to end 51b.

In a method of using the stent of the present invention, a stent andballoon catheter assembly 80 is inserted into a passageway 72, such asan artery, in a patient's body 70, as shown in FIG. 6. The assembly 80is in the deflated configuration as it is maneuvered around the curve 76in the passageway 72. The stiffness of the catheter 82 allows theassembly 80 to follow the curve 76, while the strength and stiffness ofthe stent 84 keeps it tightly engaged on the catheter balloon 86 duringinsertion. The passageway has an occlusion 74 situated at another bendin the passageway.

In FIG. 7, the stent and balloon catheter assembly 80 is shown fullyinserted into the passageway 72 so that the stent 84 and balloon 86 aresituated directly adjacent the occlusion 74 and following the curve ofthe passageway. The assembly is shown in the expanded configuration 80'in FIG. 8, in which the balloon 86' is inflated and the wire stent 84'expanded to contact and enlarge the passageway 72. The expansion isexaggerated in FIG. 8 for clarity. The assembly is expanded a sufficientamount to remove the occlusion 74 (FIG. 7) and open the passageway. Theballoon is then deflated and the catheter removed, leaving the stent tohold the passageway open.

The method of the present invention concerns a process for fabricating astent. Referring to FIG. 9, wire 30 is bent into a planar serpentineshape. The shape includes a series of straight sections 33 joined bybends or cusps 35. After the forming procedure has occurred, thestraight sections 33 become curved sections 11, and cusps 35 becomecusps 13. Also, the portions of wire 30 on either side of the centerline31 become the clockwise and counter-clockwise loops 15 and 16, asdesignated in FIG. 9. Free end 60 can be formed into a loop, such asloop 18 in FIG. 1.

A forming die 39 comprises a flat plate 40 having a straight trough 42formed therein. In the cross-sectional view of FIG. 10, it is seen thatthe trough 42 has a semi-circular surface 43. The wire 30 is placed flatupon the plate such that the centerline 31 is coincident with thecenterline of the trough 42.

The wire 30 is pressed into the trough 42 and against the semi-circularsurface 43 using a forming bar 45, as shown in FIGS. 11 and 12. Theforming bar 45 is held in place by elastic bands 46. The ends of theloops 15 and 16 project upwardly or outwardly from the trough 42 andabove the surface of the flat plate 40. In the next step of the presentmethod, pulling tools 47 are used to pull the loops 15 and 16 over theexposed surface 45a (FIG. 12) of the forming bar 45, as shown in FIGS.13 and 14. Hooks 47a at the end of pulling tools 47 engage the cusps 13of the loops 15 and 16 during this pulling step. Next, the partiallyformed stent is removed from the plate 40 by lifting the forming baraway from the plate. The bar 45 is removed, leaving the configuration ofthe partially formed stent at this point is as shown in FIG. 15.

The balloon catheter 22 is inserted through the longitudinal cylindricalopening 12 in the stent 10, as shown in FIG. 15, and the ends of theloops 15 and 16 are pressed into contact with the catheter, as shown inFIG. 3. As mentioned, when the loops 15 and 16 are in their finaloverlapping position, it is preferred that they overlap a substantialamount. In one example of the invention, this overlap 20 (FIG. 3) isabout 360 degrees. The balloon catheter used could be of variousdesigns, such as the design shown in the patent to William A. Cook, U.S.Pat. No. 4,637,396, or as available from Cook, Inc. of Bloomington,Ind., under their catalogue number OMG 4.0-4.5 and 5.3FR catheter.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative in character, it being understood that only the preferredembodiment has been shown and described.

What is claimed is:
 1. A stent comprising:a malleable wire formed into aserpentine pattern including a plurality of wire segments joined in aseries by a plurality of bends; said serpentine pattern being wrappedabout a longitudinal axis to define a hollow cylinder; said hollowcylinder having a first diameter and at least a portion of said hollowcylinder being inelastically deformable from said first diameter to asecond expanded diameter; and means, disposed within said hollowcylinder, for inelastically expanding said portion from said firstdiameter to said second expanded diameter.
 2. The stent of claim 1wherein said means for expanding is a balloon catheter.
 3. The stent ofclaim 2 having a length defined by said serpentine pattern along saidlongitudinal axis and wherein the stent includes means for maintainingsaid length substantially constant when said stent is expanded from saidfirst diameter to said second expanded diameter.
 4. The stent of claim3, wherein said means for maintaining said length includes saidplurality of wire segments oriented substantially perpendicular to saidlongitudinal axis between said bends.
 5. The stent of claim 2 whereinsaid bends are U-shaped bends.
 6. The stent of claim 5 whereinsuccessive U-shaped bends open in alternating directions.
 7. The stentof claim 6 wherein the stent has a longitudinal axis and said U-shapedbends are distributed substantially uniformly along said longitudinalaxis.
 8. The stent of claim 7 wherein the stent is longitudinallyflexible relative to a curved body passageway such that saidlongitudinal axis assumes a curved shape when positioned in a curvedbody passageway.